Common hair dryers are energized with electric power to produce heated air by means of a cord and plug thereof electrically connected to the power source. However, this kind of hair dryers are known to have following disadvantages:
1. The hair dryers can't be used in countries or districts where different power source voltages or types of sockets are not adapted. So the hair dryers may be useless if one carrying them in traveling should travel to such countries or districts.
2. The hair dryers can't be used outdoors for lack of power socket.
3. The hair dryers can't be used when main supply of power is cut off.
4. Wire inside the cord and plug may break through frequent movement of plugging in and unplugging the plug in use.